The present invention relates generally to couplings for use in motor vehicle driveline applications. More specifically, the coupling includes a hydraulic pump, a transfer clutch coupled between a pair of rotary members, and a fluid distribution system for controlling actuation of the transfer clutch.
Hydraulic couplings are used in a variety of motor vehicle driveline applications for limiting slip and transferring drive torque between a pair of rotary members. In all wheel drive applications, hydraulic couplings have been used to automatically control the transfer of drive torque from a driven member to a non-driven member in response to speed differentiation therebetween. In limited slip applications, such as used in association with a differential in an axle assembly, full-time transfer case, or transaxle, hydraulic couplings have been used to limit slip and bias the torque split between two rotary members. Examples of known hydraulic couplings which are adaptable for such driveline applications include viscous couplings, geared traction units, and passively and electronically-controlled hydraulically-actuated friction clutches generally similar to those shown and described in U.S. Pat. Nos. 5,148,900, 5,358,454, 4,649,459, 5,704,863, 5,779,013, and 6,051,903.
In response to increased consumer demand for motor vehicles with traction control systems, hydraulic couplings are currently being used in a variety of driveline applications. Such hydraulic couplings rely on hydromechanics and pressure-sensitive valve elements to passively respond to a limited range of vehicle operating conditions. These hydraulic couplings are susceptible to improvements that enhance their performance, such as a more controlled response to a wider range of vehicle operating conditions. With this in mind, a need exists to develop improved hydraulic couplings that advance the art.
Accordingly, the present invention provides a hydraulic coupling for use in motor vehicle driveline applications for rotatively coupling a pair of rotary members to limit speed differentiation and transfer drive torque therebetween.
The hydraulic coupling according to the present invention generally includes a multi-plate clutch assembly operatively connecting a pair of rotary members, an actuator assembly for actuating the clutch assembly, and a fluid control system operable for controlling actuation of the actuator assembly. The actuator assembly includes a hydraulic pump and a piston mounted in a piston chamber for movement relative to the multi-plate clutch assembly. The fluid control system regulates the fluid pressure supplied to the piston chamber by the hydraulic pump to control the clutch engagement force exerted by the piston on the clutch assembly. The fluid control system includes an electrically-controlled flow control valve operable for regulating the fluid pressure delivered to the piston chamber. Preferably, the flow control valve is a pulse-width modulated (PWM) valve having a moveable valve element. The position of the valve element is controlled by an electronic traction control module that monitors and responds to certain vehicle operating conditions including, without limitation, a sump fluid temperature, a coupling outlet oil temperature, the four wheel speeds, and the piston chamber pressure. The electronic traction control module sends a control signal to the PWM control valve for modulating the hydraulic pressure supplied to the piston chamber, which, in turn, controls clutch engagement.